Pursuant to the pre-action protocols for debt claims (2017) as laid out by the Lord Chief Justice, you have the right to ask for proof of claim and the "Claimant' has 30 Days to provide the information and if they can't provide it they must explain why not.
Look at section 5.1 and 5.2.
I have used this many times and every time it works because your using there own rules against them. Also as previously stated finish the notice (last paragraph) with: Take Notice: This is Not a complaint nor an appeal and is not to be treated as such... This stops them trying their BS before it starts and even if they still try it?
Then on the second notice (Notice of fault with opportunity to cure) you can simply point out that you have all ready given them Notice that it wasn't a complaint and that they
(assuming they haven't provided the proofs of claim by then?) are in breach of the aforementioned pre-action protocols. This makes it very difficult to try to run it into court. As you probably realise... The courts are all about following protocols. Give them an additional 14 days with the second notice and for good measure, once that has passed, send the 3rd Notice of [De]fault and give them another 7 days. Once this is done, you have been more than reasonable (3 Chances) and then it's game over. Finish off with irrevocable estoppel by acquiescence. GAME OVER!!!
https://www.justice.gov.uk/courts/procedure-rules/civil/pdf/protocols/debt-pap.pdf
